How to Solder a PCB (Through-Hole Components)

Through-hole components have leads that pass through drilled holes in the board and solder on the opposite side, this is what a standard iron handles well. Surface-mount (SMD) components sit flat on the board with no through-holes, and reworking or replacing them cleanly usually needs a hot-air rework station rather than an iron alone.

The process for each lead:

• Insert the component fully so it sits flush against the board, then bend the leads slightly outward on the underside so it doesn't fall out while you work.
• Heat the pad and the lead together for a second or two, not just the lead on its own.
• Feed solder into the heated joint until it flows around the lead and across the pad in a smooth cone.
• Remove solder, then iron, and let the joint cool without moving the component.

A bridge is excess solder accidentally connecting two pads that shouldn't be joined, more likely on boards with closely spaced pads. Use only as much solder as the joint needs, and if a bridge does form, a solder wick (braid) laid over it and heated will pull the excess solder away.

Wait until the joint has fully cooled, then trim the excess lead close to the solder joint with flush cutters. Trimming while the joint is still warm risks stressing and cracking it before it's set.